1. Field of the Invention
The present invention relates to a collision predicting operation system for an occupant protective device, such as, an air bag or sheet belt which is used with vehicles, particularly automotive vehicles.
2. Description of the Prior Art
A collision predicting operation system has been proposed in which a single wave signal is radiated into the air and its reflected wave from a target is received to produce a weal doppler signal which is reshaped, amplified and converted into a square wave through a band-pass filter, an operational amplifier and a Schmitt circuit to produce a rectangular doppler signal having a large amplitude, whereby in accordance with the timing determined by the large-amplitude doppler signal, the frequency of the wave signal is changed with time so that at least one of the change of polarity of the phase or the amount of change of the phase of the wave reflected from the target is detected to detect the distance of the target and at least one of the approaching or receding of the vehicle relative to the target is detected and thereby to detect the speed relative to the target, the distance to the target and the approaching or receding relative to the target thus performing the prediction of a collision.
A collision predicting operation system of the above type is subject to the disadvantage that the reshaping of the weak doppler system results in a voltage having a timing lag, and thus a timing error is introduced which adversely affects the accuracy in detecting the distance to the target and in detecting the approach or recession of the target.